Geological Survey Professional Paper 631 Analysis of a 24-Year Photographic Record of Nisqually Glacier, Mount Rainier National Park, Washington

PHYSIOGRAPHY

Nisqually Glacier extends from an altitude of about 14,350 feet (4,370 m) near the summit of Mount Rainier southward 4.1 miles (6.6 km) to a terminus (in 1966) at an altitude of 4,640 feet (1,410 m) for a total drop in elevation of about 9,700 feet (2,960 m). It is divided by Nisqually Cleaver into two channels from altitudes of 13,100 to 9,500 feet (3,990 to 2,900 m) in a horizontal distance of about 3,200 feet (980 m). Ice flow in the east channel is discontinuous at the steep cliffs opposite the upper part of Cowlitz Cleaver, where the ice stream is discharged in the form of intermittent avalanches or falls. If the glacier thickened sufficiently, the flow at that point would be continuous.

The glacier is fed from the west between altitudes of 8,600 and 7,100 feet (2,620 and 2,160 m) by Wilson Glacier, as shown on the maps in figure 1 and plate 1 and in the photograph in figure 34. Wilson Glacier originates in a shallow cirque and occupies a short, wide basin on the south flank of the mountain. It is fed mainly by snowfall and snow avalanches, but it also receives a minor icefall or avalanche discharge from part of an upper lobe of Kautz Glacier.

Nisqually Glacier has a surface width of approximately half a mile (0.8 km) from the foot of Nisqually Cleaver to profile 2 (pl. 1). Below profile 2 it tapers to a width of 500 feet (152 m) near the terminus. Its total area, including Wilson Glacier, was measured on the 1961 map as about 2.5 square miles (6.5 km²).

The following tabulation augments the description of the glacier by providing basic data on the locations and altitudes of several features, as taken from the 1961 map, including rough approximations of the surface slope for the reaches between those features:

Nearly 8,000 feet (2,440 m) up valley from the site of the former highway bridge and 1,200 feet (370 m) above profile 1, the glacier flows past and sometimes over a nunatak² (fig. 27). The top of the nunatak is at an altitude of 5,670 feet (1,730 m). It currently diverts a major part of the east-half ice flow toward the west wall of the canyon; for more than 10 years, from the early 1940's to the mid-1950's, essentially all the ice flow was west of the nunatak.

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²This rock hill was termed a nunatak by Giles (1960), is locally known by this name, and is so termed herein. However, this knob does not always project above the surface of the ice, nor is It always surrounded by ice, so It does not always fit the accepted glaciological definition of nunatak.

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CLIMATE

The Nisqually Glacier area receives most of its precipitation from moist, eastward-flowing cyclonic storms which form over the Pacific Ocean on the south edge of the winter Aleutian low-pressure area. More than 80 percent of this precipitation falls as snow during the period October to May. Since the low-level winds normally flow from the southwest during these winter storms, Nisqually Glacier, lying as it does on the south side of Mount Rainier, receives nearly the full effect of the storms. A precipitation shadow lies to the northeast of the mountain.

During the period 1920-59 the annual precipitation at Paradise Ranger Station (fig. 1), at an altitude of 5,430 feet (1,660 m), averaged 106 inches (269 mm) for the 24 complete but noncontinuous years of available record. On parts of the glacier, particularly at higher altitudes, the precipitation may have been greater. Snow depths at Paradise sometimes reach 30 feet (9 m). The range in annual precipitation recorded there during the 1920-59 period was from 64 to 138 inches (163 to 351 mm).